1. Field of the Invention
The invention relates to an iontophoresis device for transcutaneous administration of a medicament active principle of the anionic oligosaccharide type, and in particular of a synthetic anionic oligosaccharide having, inter alia, antithrombotic and/or anticoagulant activities.
2. Description of Related Art
Blood coagulation is a physiological phenomenon which is renowned for its complexity. Certain stimuli, such as contact activation and tissue factors, trigger the successive activation of a series of coagulation factors present in blood plasma.
Irrespective of the nature of the stimulus, the final steps are identical: activated factor X (Xa) activates factor II (also referred to as prothrombin) which, in its activated form (factor IIa, also referred to as thrombin) causes the partial proteolysis of soluble fibrinogen with the release of insoluble fibrin, the main constituent of blood clots.
Under normal physiological conditions, the activity of the coagulation factors is controlled by proteins such as antithrombin III (AT III) and heparin cofactor II (HC II), which are also present in plasma. AT III exerts an inhibiting activation on a number of coagulation factors, and in particular on factors Xa and IIa.
The inhibition of factor Xa or factor IIa therefore constitutes a preferential way of obtaining anticoagulant and antithrombotic activity, since these two factors are involved in the last two steps of coagulation, which are independent of the trigger stimulus.
The pentasaccharide of formula (I) ##STR1## with R representing --COCH.sub.3 or --SO.sub.3 has a suitable structure for binding to AT III. This compound (R=--SO.sub.3.sup.-) was obtained about ten years ago by total chemical synthesis (P. Sinay et al., Carbohydrate Research (1984), 132 C5).
Since then, a number of synthetic anionic oligosaccharides, obtained by total chemical synthesis and having antithrombotic and anticoagulant activities, have been described in the literature (cf., for example, EP-A-0,084,999, EP-A-0,113,599, EP-A-0,165,134, EP-A0,301,618, EP-A-0,454,220 and EP-A-0,529,715).
The anticoagulant and antithrombotic activities which oligosaccharides of this type can have make them useful as active principles in human therapy.
Unfortunately, because of their fairly high molecular weight, their strong anionic charge and their hydrophilic nature, they cannot be administered orally because they cannot cross the gastrointestinal barrier, and they are essentially administered parenterally, for example subcutaneously or intravenously.
It is known that, in such a case, a possible alternative to parenteral administration is transdermic administration, since the compounds do not need to pass through the gastrointestinal tract. However, it has been observed that oligosaccharides of the aforementioned type do not penetrate the skin at a fast enough rate for the systemic concentrations to reach effective therapeutic values.
It is known that iontophoresis can allow certain active principles to be administered transcutaneously to a subject, these active principles generally consisting of compounds having low molecular weight and ionic nature.
To do this, operation is carried out with an aqueous solution or an aqueous gel holding the active principle in an at least partially ionized form, and an electrical signal is applied between, on the one hand, a first electrode, referred to as the active electrode, having the same polarity as the ions of the active principle to be administered and located in contact with a reservoir element which holds the active principle and is placed in contact with a first area of the subject's skin, and on the other hand a second electrode, referred to as the back electrode or passive electrode, having the opposite polarity to the one associated with the active principle, which is placed in contact, directly or via an indifferent electrolyte, with a second area of the subject's skin which is different from the first area. When a current, generated by application of the electrical signal between the electrodes, passes through the circuit produced in this way, the ions of the active principle migrate away from the electrode having the same polarity (active electrode), through the subject's skin and tissue, to the electrode of opposite polarity (back electrode) and are in this way passed into the subject's circulatory system.